Disk drives generally utilize rotary actuators to position one or more magnetic read/write heads (also known as transducers), with respect to a similar number of magnetic disks rotatably mounted on a hub driven by a motor. The read/write heads are moved across selected tracks of the magnetic disks to gain access to the digital information recorded on the tracks and/or to write data to particular locations on the tracks. The read/write heads are mounted on an air bearing slider. The slider positions the read/write heads above the data surface of the corresponding disk by a cushion of air generated by the rotating disk. Alternatively, the slider may operate in contact with the surface of the disk. The slider is mounted to a suspension load beam. The suspension maintains the read/write heads and the slider adjacent to or in contact with the data surface of the disk.
The suspension is connected to the distal end of an actuator arm that is pivotally installed within the housing of the disk drive. Typically, the actuator arm is mounted to a pivot bearing assembly that allows the actuator arm to rotate or pivot in response to torques generated by a voice coil motor mounted to the yoke portion of the actuator arm.
The voice coil is integrated within a closed loop feedback system or servo system to dynamically position the heads directly over the desired data tracks. The principle of operation for the voice coil motor is controlled electromagnetic interaction between a coil and a permanent magnet. The voice coil typically includes a bundle of wires or coils that are mounted to the yoke arms that extend away from the central pivot axis of the actuator. The coil is immersed in an axially oriented bi-polar magnetic field generated by one or more permanent magnets positioned directly adjacent the coil. When a current is applied to the coil, a force is generated on the coil. By precisely controlling the current, positioning of the heads is achieved. The simplicity yet effectiveness of a voice coil comprising the coil of wires and the magnetic field makes such motors ideal for disk drives in terms of precise head positioning. However, the required orientation of the coils with respect to the magnets requires the actuator to have a somewhat elongated configuration to accommodate mounting of the coils to the yoke. Thus, the disk drive has a definable constraint in terms of size to account for the configuration of the actuator.
As disk drive technology continues to develop, there is a continuing need to provide reliable yet preferably smaller and less mechanically/electrically complex assemblies which enables manufacturers to more economically produce such drives.
While voice coil motors have proven to be effective for use in many disk drive applications, it would be advantageous to provide a motor to control actuator movement wherein part count and assembly complexity is reduced, yet standards of performance are maintained to handle the ever increasing track densities found on many data disks. Additionally, there is a need to provide such actuator control by use of a motor that is smaller in size, yet can handle the necessary torque requirements for precise actuator positioning.